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Fri, 25 Sep 2020 06:46:32 -0400 X-MC-Unique: iK4vulDwOIyr9Lo3i97nNw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 77BEB800E23; Fri, 25 Sep 2020 10:46:30 +0000 (UTC) Received: from [10.36.112.211] (ovpn-112-211.ams2.redhat.com [10.36.112.211]) by smtp.corp.redhat.com (Postfix) with ESMTP id DC7735D9E2; Fri, 25 Sep 2020 10:46:28 +0000 (UTC) Subject: Re: [PATCH 8/9] mm, page_alloc: drain all pcplists during memory offline To: Vlastimil Babka , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, Michal Hocko , Pavel Tatashin , Oscar Salvador , Joonsoo Kim References: <20200922143712.12048-1-vbabka@suse.cz> <20200922143712.12048-9-vbabka@suse.cz> From: David Hildenbrand Autocrypt: addr=david@redhat.com; prefer-encrypt=mutual; keydata= mQINBFXLn5EBEAC+zYvAFJxCBY9Tr1xZgcESmxVNI/0ffzE/ZQOiHJl6mGkmA1R7/uUpiCjJ dBrn+lhhOYjjNefFQou6478faXE6o2AhmebqT4KiQoUQFV4R7y1KMEKoSyy8hQaK1umALTdL QZLQMzNE74ap+GDK0wnacPQFpcG1AE9RMq3aeErY5tujekBS32jfC/7AnH7I0v1v1TbbK3Gp XNeiN4QroO+5qaSr0ID2sz5jtBLRb15RMre27E1ImpaIv2Jw8NJgW0k/D1RyKCwaTsgRdwuK Kx/Y91XuSBdz0uOyU/S8kM1+ag0wvsGlpBVxRR/xw/E8M7TEwuCZQArqqTCmkG6HGcXFT0V9 PXFNNgV5jXMQRwU0O/ztJIQqsE5LsUomE//bLwzj9IVsaQpKDqW6TAPjcdBDPLHvriq7kGjt WhVhdl0qEYB8lkBEU7V2Yb+SYhmhpDrti9Fq1EsmhiHSkxJcGREoMK/63r9WLZYI3+4W2rAc UucZa4OT27U5ZISjNg3Ev0rxU5UH2/pT4wJCfxwocmqaRr6UYmrtZmND89X0KigoFD/XSeVv jwBRNjPAubK9/k5NoRrYqztM9W6sJqrH8+UWZ1Idd/DdmogJh0gNC0+N42Za9yBRURfIdKSb B3JfpUqcWwE7vUaYrHG1nw54pLUoPG6sAA7Mehl3nd4pZUALHwARAQABtCREYXZpZCBIaWxk ZW5icmFuZCA8ZGF2aWRAcmVkaGF0LmNvbT6JAlgEEwEIAEICGwMGCwkIBwMCBhUIAgkKCwQW AgMBAh4BAheAAhkBFiEEG9nKrXNcTDpGDfzKTd4Q9wD/g1oFAl8Ox4kFCRKpKXgACgkQTd4Q 9wD/g1oHcA//a6Tj7SBNjFNM1iNhWUo1lxAja0lpSodSnB2g4FCZ4R61SBR4l/psBL73xktp rDHrx4aSpwkRP6Epu6mLvhlfjmkRG4OynJ5HG1gfv7RJJfnUdUM1z5kdS8JBrOhMJS2c/gPf wv1TGRq2XdMPnfY2o0CxRqpcLkx4vBODvJGl2mQyJF/gPepdDfcT8/PY9BJ7FL6Hrq1gnAo4 3Iv9qV0JiT2wmZciNyYQhmA1V6dyTRiQ4YAc31zOo2IM+xisPzeSHgw3ONY/XhYvfZ9r7W1l pNQdc2G+o4Di9NPFHQQhDw3YTRR1opJaTlRDzxYxzU6ZnUUBghxt9cwUWTpfCktkMZiPSDGd KgQBjnweV2jw9UOTxjb4LXqDjmSNkjDdQUOU69jGMUXgihvo4zhYcMX8F5gWdRtMR7DzW/YE BgVcyxNkMIXoY1aYj6npHYiNQesQlqjU6azjbH70/SXKM5tNRplgW8TNprMDuntdvV9wNkFs 9TyM02V5aWxFfI42+aivc4KEw69SE9KXwC7FSf5wXzuTot97N9Phj/Z3+jx443jo2NR34XgF 89cct7wJMjOF7bBefo0fPPZQuIma0Zym71cP61OP/i11ahNye6HGKfxGCOcs5wW9kRQEk8P9 M/k2wt3mt/fCQnuP/mWutNPt95w9wSsUyATLmtNrwccz63W5Ag0EVcufkQEQAOfX3n0g0fZz Bgm/S2zF/kxQKCEKP8ID+Vz8sy2GpDvveBq4H2Y34XWsT1zLJdvqPI4af4ZSMxuerWjXbVWb T6d4odQIG0fKx4F8NccDqbgHeZRNajXeeJ3R7gAzvWvQNLz4piHrO/B4tf8svmRBL0ZB5P5A 2uhdwLU3NZuK22zpNn4is87BPWF8HhY0L5fafgDMOqnf4guJVJPYNPhUFzXUbPqOKOkL8ojk CXxkOFHAbjstSK5Ca3fKquY3rdX3DNo+EL7FvAiw1mUtS+5GeYE+RMnDCsVFm/C7kY8c2d0G NWkB9pJM5+mnIoFNxy7YBcldYATVeOHoY4LyaUWNnAvFYWp08dHWfZo9WCiJMuTfgtH9tc75 7QanMVdPt6fDK8UUXIBLQ2TWr/sQKE9xtFuEmoQGlE1l6bGaDnnMLcYu+Asp3kDT0w4zYGsx 5r6XQVRH4+5N6eHZiaeYtFOujp5n+pjBaQK7wUUjDilPQ5QMzIuCL4YjVoylWiBNknvQWBXS lQCWmavOT9sttGQXdPCC5ynI+1ymZC1ORZKANLnRAb0NH/UCzcsstw2TAkFnMEbo9Zu9w7Kv AxBQXWeXhJI9XQssfrf4Gusdqx8nPEpfOqCtbbwJMATbHyqLt7/oz/5deGuwxgb65pWIzufa N7eop7uh+6bezi+rugUI+w6DABEBAAGJAjwEGAEIACYCGwwWIQQb2cqtc1xMOkYN/MpN3hD3 AP+DWgUCXw7HsgUJEqkpoQAKCRBN3hD3AP+DWrrpD/4qS3dyVRxDcDHIlmguXjC1Q5tZTwNB boaBTPHSy/Nksu0eY7x6HfQJ3xajVH32Ms6t1trDQmPx2iP5+7iDsb7OKAb5eOS8h+BEBDeq 3ecsQDv0fFJOA9ag5O3LLNk+3x3q7e0uo06XMaY7UHS341ozXUUI7wC7iKfoUTv03iO9El5f XpNMx/YrIMduZ2+nd9Di7o5+KIwlb2mAB9sTNHdMrXesX8eBL6T9b+MZJk+mZuPxKNVfEQMQ a5SxUEADIPQTPNvBewdeI80yeOCrN+Zzwy/Mrx9EPeu59Y5vSJOx/z6OUImD/GhX7Xvkt3kq Er5KTrJz3++B6SH9pum9PuoE/k+nntJkNMmQpR4MCBaV/J9gIOPGodDKnjdng+mXliF3Ptu6 3oxc2RCyGzTlxyMwuc2U5Q7KtUNTdDe8T0uE+9b8BLMVQDDfJjqY0VVqSUwImzTDLX9S4g/8 kC4HRcclk8hpyhY2jKGluZO0awwTIMgVEzmTyBphDg/Gx7dZU1Xf8HFuE+UZ5UDHDTnwgv7E th6RC9+WrhDNspZ9fJjKWRbveQgUFCpe1sa77LAw+XFrKmBHXp9ZVIe90RMe2tRL06BGiRZr jPrnvUsUUsjRoRNJjKKA/REq+sAnhkNPPZ/NNMjaZ5b8Tovi8C0tmxiCHaQYqj7G2rgnT0kt WNyWQQ== Organization: Red Hat GmbH Message-ID: Date: Fri, 25 Sep 2020 12:46:27 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.11.0 MIME-Version: 1.0 In-Reply-To: <20200922143712.12048-9-vbabka@suse.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 22.09.20 16:37, Vlastimil Babka wrote: > drain_all_pages() is optimized to only execute on cpus where pcplists are not > empty. The check can however race with a free to pcplist that has not yet > increased the pcp->count from 0 to 1. Make the drain optionally skip the racy > check and drain on all cpus, and use it in memory offline context, where we > want to make sure no isolated pages are left behind on pcplists. > > Signed-off-by: Vlastimil Babka > --- > include/linux/gfp.h | 1 + > mm/memory_hotplug.c | 4 ++-- > mm/page_alloc.c | 29 ++++++++++++++++++++--------- > 3 files changed, 23 insertions(+), 11 deletions(-) > > diff --git a/include/linux/gfp.h b/include/linux/gfp.h > index 67a0774e080b..cc52c5cc9fab 100644 > --- a/include/linux/gfp.h > +++ b/include/linux/gfp.h > @@ -592,6 +592,7 @@ extern void page_frag_free(void *addr); > > void page_alloc_init(void); > void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp); > +void __drain_all_pages(struct zone *zone, bool page_isolation); > void drain_all_pages(struct zone *zone); > void drain_local_pages(struct zone *zone); > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 08f729922e18..bbde415b558b 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1524,7 +1524,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) > goto failed_removal; > } > > - drain_all_pages(zone); > + __drain_all_pages(zone, true); > > arg.start_pfn = start_pfn; > arg.nr_pages = nr_pages; > @@ -1588,7 +1588,7 @@ int __ref offline_pages(unsigned long start_pfn, unsigned long nr_pages) > */ > ret = test_pages_isolated(start_pfn, end_pfn, MEMORY_OFFLINE); > if (ret) > - drain_all_pages(zone); > + __drain_all_pages(zone, true); > } while (ret); > > /* Mark all sections offline and remove free pages from the buddy. */ > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 4e37bc3f6077..33cc35d152b1 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -2960,14 +2960,7 @@ static void drain_local_pages_wq(struct work_struct *work) > preempt_enable(); > } > > -/* > - * Spill all the per-cpu pages from all CPUs back into the buddy allocator. > - * > - * When zone parameter is non-NULL, spill just the single zone's pages. > - * > - * Note that this can be extremely slow as the draining happens in a workqueue. > - */ > -void drain_all_pages(struct zone *zone) > +void __drain_all_pages(struct zone *zone, bool force_all_cpus) > { > int cpu; > > @@ -3006,7 +2999,13 @@ void drain_all_pages(struct zone *zone) > struct zone *z; > bool has_pcps = false; > > - if (zone) { > + if (force_all_cpus) { > + /* > + * The pcp.count check is racy, some callers need a > + * guarantee that no cpu is missed. > + */ > + has_pcps = true; > + } else if (zone) { > pcp = per_cpu_ptr(zone->pageset, cpu); > if (pcp->pcp.count) > has_pcps = true; > @@ -3039,6 +3038,18 @@ void drain_all_pages(struct zone *zone) > mutex_unlock(&pcpu_drain_mutex); > } > > +/* > + * Spill all the per-cpu pages from all CPUs back into the buddy allocator. > + * > + * When zone parameter is non-NULL, spill just the single zone's pages. > + * > + * Note that this can be extremely slow as the draining happens in a workqueue. > + */ > +void drain_all_pages(struct zone *zone) > +{ > + __drain_all_pages(zone, false); > +} > + > #ifdef CONFIG_HIBERNATION > > /* > Interesting race. Instead of this ugly __drain_all_pages() with a boolean parameter, can we have two properly named functions to be used in !page_alloc.c code without scratching your head what the difference is? (yeah, coming up with a proper name is difficult. the one gives more guarantees than the other, that cannot really be deducted from "force_all_cpus" - maybe we can encode the actual semantics in the name) -- Thanks, David / dhildenb